1. Field of the Invention
The invention pertains to vehicle traffic control and more particularly to the control of merging vehicles travelling along intersecting guideways.
2. Description of the Prior Art
Automated mass transit systems require devices for controlling the flow of traffic along the guideways of the system and for controlling traffic flow at a merge or intersection of two of these guideways. Traffic control along a guideway may be accomplished with the utilization of collision avoidance apparatus on-board each vehicle, such as the device disclosed by Cronson et al. in U.S. Pat. No. 4,254,418 issued Mar. 3, 1981 and assigned to the assignee of the present invention, which may be utilized to maintain minimum separation between vehicles in a guideway, thus avoiding collision and controlling the flow of traffic. This collision avoidance apparatus utilizes a short pulse transmitter and receiver on each vehicle that traverses the guideway. A short pulse is coupled from the transmitter to a transmission line, which parallels the guideway, for propagation forward of the vehicle. When the short pulse reaches a preceding vehicle it is reflected from a reflector positioned at the rear of the forward vehicle back towards the emitting vehicle where it is received and processed. Since reflections from a preceding vehicle are required, this apparatus cannot provide information for controlling the flow of vehicles approaching an intersection of two guideways or approaching a merge of two guideways to safely combine these vehicles into a single line of traffic.